Electric contact switching device

ABSTRACT

A high frequency R-F switch includes a switch body of housing made from a conductive material or a non-conductive resin having a conductive layer plated on the body surfaces. The switching device includes a first external connector, a first conductor having a switching contact member connected to the first external connector for switching a connection with the switch contact member. A conductive housing .[.supports.]. .Iadd.houses .Iaddend.the first conductor, .Iadd.and connects to .Iaddend.a second external connector and second conductor. The switch body or housing is in electrical connection with the second external conductor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of .[.our copending application.]..Iadd.reissue application Ser. No. 07/769,497, filed Oct. 1, 1991, nowabandoned, which was a continuation of reissue application Ser. No.07/642,550, filed Jan. 18, 1991, now abandoned, which was a continuationof reissue application Ser. No. 07/512,016, filed Apr. 16, 1990, nowabandoned, which was a continuation of reissue application Ser. No.07/307,248, filed Feb. 7, 1989, now abandoned, which was a continuationof reissue application Ser. No. 07/008,431, filed Jan. 29, 1987, nowabandoned, for reissue of U.S. Letters Patent No. 4,496,806, issued Jan.29, 1985, on Ser. No. 06/529,229, filed Sep. 6, 1983, which was acontinuation of .Iaddend.Ser. No. .Iadd.06/.Iaddend.343,832, filed Jan.15, 1982, now abandoned.

BRIEF SUMMARY OF THE INVENTION

This invention relates to an electric contact switching devicecomprising a contact switching mechanism and a housing member supportingthe electric switching mechanism, and more particularly to an improvedswitching device capable of switching high-frequency signals.

Generally, a conventional electric contact switching device designed forswitching low-frequency signals cannot be used as a high-frequencysignal switching device because a desired isolation in transmissionlines cannot be performed, unnecessary radiation occurs within thedevice, and its gain is extremely attenuated. A high-frequency contactswitching device is well known which includes a metal shielding housingfor enclosing a switching mechanism and is constructed in a coaxialconfiguration. Such a conventional high-frequency contact switchingdevice, however, has the disadvantage that the metal housing must bemade of an expensive material with a carefully tooled machine.

It is, therefore, a primary object of this invention to provide anelectric contact switching device which is easy to assemble at a lowcost and capable of performing an improved switching operation not onlywith respect to low-frequency signals but also with respect tohigh-frequency signals.

It is a further object of this invention to provide an electric contactswitching device which can provide a good isolation of high-frequencysignals.

It is another object of this invention to provide an electric contactswitching device which includes a contact switching mechanism forconnection to an inner conductor of an external coaxial cable and amolded base member carrying an electrically conductive member forconnection to an outer conductor of the cable. According to thisinvention, there is provided an electric contact switching devicecomprising first external connecting means, first conductor means havinga switching contact member connected to the first external connectingmeans for switching a connection with the switching contact member,housing means for supporting and housing the first conductor means,second external connecting means, and second conductor means connectedto the second external connecting means, the second conductor meansbeing disposed on a predetermined surface of the housing means.

Other objects and numberous advantages of the electric contact switchingdevice according to this invention will become apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings, in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective disassembled view of an electric contactswitching device as a preferred embodiment of this invention;

FIG. 2 is a top plan assembled sectional view showing the switchingdevice of FIG. 1;

FIG. 3 is a fragmentary sectional detailed view for illustrating anelectrically conductive member disposed on a base member of theswitching device of FIG. 2;

FIG. 4 is a side sectional view of the device of FIG. 2;

FIG. 5A is a side assembled sectional view of an electrical contactswitching device as a modification of the embodiment of FIG. 1;

FIG. 5B is a sectional view illustrating an external terminal which isemployed in the device of FIG. 5A;

FIG. 5C is a sectional view illustrating a modified external terminalwhich is employed in the device of FIG. 5A;

FIG. 6A is a side assembled sectional view of an electrical contactswitching device as another modification of the device of FIG. 1;

FIGS. 6B and 6C show modified external terminals which may be employedin the device of FIG. 6A;

FIG. 7 is a perspective disassembled view of an electric contactswitching device as another embodiment of this invention;

FIG. 8 is a top plan assembled view showing the device of FIG. 7; and

FIG. 9 is a side assembled sectional view of the device of FIG. 7.

DETAILED DESCRIPTION

Referring, now, to FIGS. 1, 2 and 4 there is shown an electric contactswitching device as a preferred embodiment of this invention. Theelectric contact switching device includes a base member 40, a contactswitching mechanism 50 housed within and supported by the base member40, and a cover member 23 mounted on the base member 40.

The base member 40 includes a base 1 and external terminals 12 and 13secured thereto. The base 1 is a molded plastic, and may be made of anon-crystalline thermoplastic resin such as polysulphone, athermosetting resin such as polyethersulphone, or ABS resin. Asillustrated in FIG. 3, the base 1 is covered with an electricallyconductive layer 11 by plating, electroplating, vacuum vapor deposition,coating with an appropriate paint or the like. The layer 11 iselectrically connected to terminals 12 and 13. The base 1 includes holes2, 3 and 4 which extend vertically therethrough, and at a side medialposition thereof a recessed portion 1a. A resetting spring 5 is insertedinto the portion 1a. The base 1 further includes grooves 8 and 9 intowhich cards or slidable members 6 and 7. Thus, the holes 2, 3 and 4 andthe grooves 8 and 9 provide a recessed portion 10 for housing theswitching mechanism 50. Inner conductors 15, 16 and 17 are supported bydielectric blocks 18, 19 and 20, and inserted into the holes 2, 3 and 4,respectively. The inner conductors 15, 16 and 17 serve at the bottomportions thereof as external terminals, and at the upper portionsthereof as stationary contacts 15a, 16a and 17a, respectively. Thus, theinner conductors, 15, 16 and 17 and the conductive layer 11 areinsulated from each other through blocks 18, 19 and 20 in view of d.c.,and compose a predetermined circuit impedance or distributed constant.

The cards 6 and 7, respectively, carry movable contact blades 21 and 22,and are at the ends thereof biased by spring 5 as illustrated in FIG. 2.Then, the blade 21 contacts an inner wall of the base 1 covered withconductive layer 11 (see FIG. 3), but the blade 22 short-circuits thestationary contacts 16a and 17a. As illustrated in FIG. 4, the covermember 23 of electrically conductive material is fixedly mounted on anupper surface of base 1 by a clip or the like, and electricallyconnected to the layer 11.

If the cards 6 and 7 are pushed against the spring 5 by an actuator (notshown) which is manually, mechanically or electromagnetically operated,the blade 21 short-circuits the contacts 15a and 16a and the blade 22contacts the conductive layer 11 disposed on an inner wall of thebase 1. Thus, inner conductors 15, 16 and 17, respectively, serve asnormally-open, common and normally-closed terminals of this electricalcontact switching device.

Though the base 1 of insulating material has on its surface a conductivelayer of the layer 11, a high-frequency current can concentratedly flowthrough the layer 11 according to its skin effect, whereby isolation asto high-frequency signals can be performed. Though the base 1 is made ofinsulating resin in this embodiment, it may alternatively be a ceramicor conductive resin member. When the base 1 is made of a conductiveresin, such as a polyester or polytetrafluoroethylene containing carbonor iron dust, a silicone rubber containing silver, aluminium or copperdust, or the like, the conductive layer 11 is intimately connected tothe base 1 through the conductive dust contained therein, particularlywhen the layer 11 is formed by electroplating. Such conductive base (1)improves the conductivity of the external terminals 12 and 13 with layer11. As compared with the metal housing body employed in the conventionaldevice, the base 1 made of the above-mentioned material is easy to befabricated at a reduced cost and can provide a switching device ofreduced weight.

The layer 11 is disposed on the inner wall surface of the base 1 so asto contact with movable contact blade 21 or 22 in a contact-breakposition, whereby any high-frequency short circuit cannot be produced byelectrostatic coupling among stationary contacts 16a and 15a (17a) andconductive layer 11 through movable blade 21 (22). In other words,excellent isolation as to high-frequency signals can be obtained withoutincreasing the stroke of the blades 21 and 22, and the switching devicein this embodiment can be miniaturized.

According to this embodiment, there is provided an electric contactswitching device including first external connecting members, (15, 16and 17), first conducutor members (15a, 16a, 17a, 21 and 22), housingmembers (1 and 23), second external connecting member (12, 13) andsecond conductor member (11). The first external connecting members (15to 17) are designed to be connected to a signal line of a low-frequencycable or an inner conductor of a high-frequency coaxial cable, and thesecond external connecting member (12, 13) is designed to be connectedto a ground line of the low-frequency cable or an outer conductor of thecoaxial cable.

Though the conductive layer 11 in this embodiment is disposed on all ofthe surfaces of the base 1, it may be locally disposed as long as itsatisfies circuit design requirements, such as circuit impedance,voltage standing wave ratio, distributed constant, shielding and soforth. For instance, the conductive layer 11 may be disposed only on thesurfaces of inner walls of the base 1, in which external terminals 12and 13 desirably extend through base 1 (as illustrated by terminals 147in FIG. 9) for connection with the layer 11. For switchinghigh-frequency signals, e.g., 1 giga hertz, the layer 11 may belimitedly disposed on one wall of base 1 in parallel with the blades 21and 22, in which layer 11 is connected with terminals 12 and 13 througha certain connection lead. The layer 11 is effective for shielding theswitching mechanism 50 from external noise, but the minimum portion ofthe base 1 which should be covered with the layer 11 depends on thefrequency of signals applied to this switching device. The cover member23 is made of a conductive metal material but it may be of an insulatingplastic.

If desired, the member 23 may be omitted. If the recessed portion 10 isfairly deep and surrounded with conductive layer 11, whether the member23 is conductive or not does not affect the high-frequencycharacteristic of this device.

Returning to FIG. 5A there is shown an electric contact switching deviceas a modification of the embodiment of FIG. 1. In FIG. 5A the externalterminals 12 and 13 embedded into the base 1 as shown in FIG. 4 arerepresented by projections 12a and 13a which are molded with base 1 as asingle unit and plated with conductive layer 11 as illustrated in detailin FIG. 5B. The layer 11 not only provides conductivity in the terminals12a and 13a, but also reinforces the same. Since the parts of theterminals 12a and 13a are simultaneously formed with the base 1 and notrequired to be assembled with the same, the assembling work issimplified and a good conductivity between terminal 12a (13a) andconductive layer 11 is ensured.

In FIG. 5C, there is shown an improved external terminal 12b (13b) whichis a modification of the terminal 12a (13a). When the switching deviceof FIG. 5A is mounted on a printed circuit board and the terminals 12aand 13a are soldered, a high temperature is applied to the terminals 12aand 13a. If the terminals 12a and 13a are made of synthetic resin suchas ABS resin and are heated, the resin becomes soft and produces gasseswithin the conductive layer 11 coating the terminals 12a and 13a so asto explode the terminals 12a and 13a. The terminal 12b (13b) of FIG. 5Chas a recessed bottom end and is covered with an electroless platinglayer 11a and an electroplating layer 11b. The electroless plating layer11a is a nickel or copper plating layer 0.2 to 0.5 microns thick, anduniformly formed on all of the surfaces of the base 1 including therecessed portion of terminal 12b (13b). Then, the electroplated layer11b of nickel or the like which is easy to be soldered with solder isformed on the layer 11a except the recessed portion of the terminal 12b(13b). Therefore, even if the terminal 12b (13b) becomes soft on heatingand produces gasses therewithin, the recessed portion only is easy to bebroken so as to exhaust the pressured gasses, and the terminal 12b (13b)is not destroyed by heat of soldering. For this purpose, the bottomportion of the terminal 12a (13a) shown in FIG. 5B may be cut off afterforming the layer 11, or left unplated.

If the electric contact switching device in the foregoing description isused in such a manner that the external terminals (12, 13) as outerconductor terminals or ground terminals are not needed because of theperipheral condition of circuits or parts connected with this device,the external terminals (12, 13) may be omitted. For instance, a socketfor receiving the switching device is designed to contact a flat platedexternal surface portion of the base 1 for connection with the platedlayer 11, the projecting terminals (12, 13) may be omitted.Particularly, unless the device is used for switching high-frequencysignals, such projecting ground terminals (12, 13) are not necessary.

FIG. 6A illustrates an electric contact switching device as anothermodification of the embodiment of FIG. 4. The device of FIG. 6A isdesigned for connection with coaxial cables, and includes outerconnecting terminals 41, 42 and 43 which are molded with base 1 as asingle unit and plated with a conducting layer (not shown). Therespective terminals 41, 42 and 43 can be directly connected withconnectors of coaxial cables. FIGS. 6B and 6C illustrate modifiedexternal terminals for connection with connectors of external coaxialcables. In FIG. 6B the molded base 1 includes a cylindrical projection70 on which a threaded metal sleeve 60 is tightly mounted. The sleeve 60may be mounted on the projection 70 which is plated with a conductivelayer (not shown). Alternatively, the conductive layer may be platedafter mounting the sleeve 60 on the projection 70. In FIG. 6C a sleeve61 is inserted and secured into a recessed portion 71 of base 1 which isformed in a hole 3a for supporting a dielectric block 19 carrying aninner conductor 16. A conductive layer (not shown) may be disposed onthe base 1 before or after insertion by sleeve 61 to the base 1.

Returning to FIGS. 7 to 9 there is illustrated an electric contactswitching device, viz., an electromagnetic relay, as another embodimentof this invention. A base or housing 110 is a box-shaped molded plastic,and all of the surfaces thereof are plated with a conductive material(not shown). The conductive plating layer covering the base 110reinforces the base 110. The base 110 includes a separating wall 111 tothereby provide a pair of compartments 112 and 113. An electromagnetic114 is disposed within the compartment 112 of base 110, which includeson iron core 115, a spool 116, a coil 117, and an L-shaped yoke securedto the core 115. A pair of leads 119 and 120 are embedded in the spool116, and are piercing through a bottom wall portion 121 of base 110. AnL-shaped movable lever 122 is pivotally supported by a hinge spring 123with respect to an edge portion 118a of the yoke 118. The spring 123 atits base end 123a is mounted on a pair of (upper and lower) recessedportions 118b of the yoke 118. An L-shaped fixing member 124 is engagedwith the yoke 118 and inserted into a vertically grooved portion 125formed in the base 110 so as to fix the yoke 118 to the bottom wallportion 121.

A resetting leaf spring 126 is inserted within the compartment 112 so asto be engaged with a pair of projections 131a and 131b and be biased bythe lever 122 at its end portion 122c. A pair of cards 127 and 128 attheir engaging portions 127a and 128a are engaged with a pair ofactuating portions 129 and 130 of the lever 122.

The cards 127 and 128 are slidably guided by a pair of grooves 134 and135 formed in the compartment 113 of the base 110. The card 127 carriesa movable contact blade 139 for switching a circuit across stationarycontact members 136 and 137. The card 128 carries a movable contactblade 140 for switching a circuit across stationary contact members 137and 138. Dielectric blocks 141, 142 and 143 supporting contact members136, 137 and 138 are inserted into holes 144, 145 and 146 formed in thebottom wall portion 121 of base 110 as illustrated in FIG. 9. Outerconductor lead terminals 147 are inserted into holes 150 extendingthrough the bottom portion 121 of base 110 so as to block any highfrequency current flow between terminal portions 136a and 137a ofmembers 136 and 137 and between terminal portions 137a and 138a ofmembers 137 and 138. The holes 150 on their inner surfaces are coatedwith a conductive layer-forming material not shown extending over all ofthe surfaces of the base 110 for electrical connection with terminals147. A metal plate 160 is mounted over the compartment 113 as ashielding member, and an upper cover 152 is mounted on the base 110 asillustrated in FIG. 9. The cover 152 is a molded plastic having aseparating wall 154 confronting the wall 111 of the base 110. The cover152 further has projections 155 and 156 for ensuring the slidingmovement of the cards 127 and 128. Though the cover 152 is not coveredwith a conductive layer, it may be metal-plated as a shielding member.The plate 160 may be omitted, if desired.

In the above-mentioned construction, if the coils 117 is energized, thelever 122 is attracted by the core 115. Then, the end portion 122c ofthe attracted lever 122 pushes the spring 126 in the direction of thesolid arrow-mark shown in FIG. 8, and the cards 127 and 128 areforwardly moved by the spring 126 through its portions 120 and 130.Accordingly, the blade 139 leaves from the contact members 136 and 137and the blade 140 contacts the contact members 137 and 138. That is, theconnection with the common contact 137 is switched from the breakcontact 136 to the make contact 138. If the coil 117 is.[.disenergized.]. .Iadd.deenergized.Iaddend., the blades 139 and 140return to their original positions illustrated in FIG. 8.

Normally, the blade 140 contacts projections 149a and 149b formed in thebase 110. When the coil 117 is energized, the blade 139 contactsprojections 148a and 148b. The projections 148a, 148b, 148c, 149a, 149band 149c have conductive layers extending to the terminals 147.Therefore, the blades 139 and 140 are prevented from making anyunnecessary high-frequency short circuit among contact members 136, 137and 138.

Alternatively, the blades 139 and 140 may be assembled in such a mannerthat normally the blade 139 contacts the projections 149c and 149a andthe blade 140 contacts the members 137 and 138, while when the coil 117is energized, the blade 139 contacts the members 136 and 137 and theblade 140 contacts the projections 148b and 148c. Thus, by changing theinserting position for the blades 139 and 140, the switching mode ofthis relay can be reversed.

Though the switching device in this embodiment is designed for ahigh-frequency switch of giga hertz order, it may be used as a d.c. orlow-frequency switch. The switching device in this embodiment may bemodified so that the respective cards 127 and 128 carry a plurality ofblades so as to provide a switching device which switches a plurality ofcircuits.

Thus, according to this invention there is provided an electric contactswitching device including a switching mechanism having inner conductorsfor switching a connecting circuit therewithin, a base member forsupporting and housing the switching mechanism, and an outer conductordisposed on a predetermined portion of a surface of the base member.Since the outer conductor is plated on the fixed base member, thecircuit design of the switching device is simplified. This isadvantageous for a high-frequency circuit.

It will be understood from the foregoing description that this inventionis applicable to another modified electric contact switching device.This invention may be applied to an electric contact switching deviceincluding a flat-shaped base member for supporting a switching mechanismhaving an inner conductor, a housing body which is mounted on orencloses the flat-shaped base member, and an outer conductor which isdisposed on a predetermined surface of the base member and/or thehousing body and connected to an external member disposed on the device.

It should be understood that the above description is merelyillustrative of this invention and that many changes and modificationsmay be made by those skilled in the art without departing from the scopeof the appended claims.

What is claimed is:
 1. An electric contact switching device whichconfines R-F within said device comprising in combination:first externalconnecting means; dielectric means for supporting said first externalconnecting means; first conductor means having a switching contactmember connected to said first external connecting means for switching afirst connection with said switching contact member; housing means forsupporting and housing said first conductor means, and said dielectricmeans wherein said housing is constructed from a material which is anelectrically conductive resin; second external connecting means; secondconductor means connected to said second external connecting means; andsaid second conductor means being in electrical contact with saidhousing means.
 2. An electric contact switching device according toclaim 1, wherein said housing means consists of a molded base membersupporting said first conductor means and a cover member covering saidbase member.
 3. An electric contact switching device according to claim1, wherein said first conductor means is a switching mechanismcomprising a stationary contact member and a movable contact blademember, said second conductor means being disposed on a predeterminedsurface of said housing means so as to contact with said movable contactblade member in a break circuit position thereof.
 4. An electric contactswitching device according to claim 1 which further includes aconductive plate member, and in which said housing means includes arecessed portion for housing said first conductor means, said conductiveplate member being mounted on said recessed portion and connected tosaid second conductor means.
 5. An electric contact switching deviceaccording to claim 1, wherein said second external connecting means is ametal cylindrical member fixed to said housing means and connected withsaid second conductor means.
 6. An electric contact switching deviceaccording to claim 1 further comprising electromagnet means housedwithin said housing means so as to actuate said first conductor means.7. An electric contact switching device which confines .[.said.]. R-Fwithin said device comprising in combination:first external connectingmeans; dielectric means for supporting said first external connectingmeans; first conductor means having a switching contact member connectedto said first external connecting means for switching a first connectionwith said switching contact member; housing means for supporting andhousing said first conductor means and said dielectric means, whereinsaid housing is constructed from an insulating material having aconductive material on the surfaces thereof; second external connectingmeans; .Iadd.and .Iaddend. second conductor means connected to saidsecond external connecting .Iadd.means.Iaddend.; .[.and.]. said secondconductor means being in electrical contact with said conductivematerial plated on said housing means.
 8. An electric contact switchingdevice according to claim 7, wherein said housing means consists of amolded base member supporting said first conductor means and a covermember covering said base member.
 9. An electric contact switchingdevice according to claim 7, wherein said first conductor means is aswitching mechanism comprising a stationary contact member and a movablecontact blade member, said second conductor means being disposed on apredetermined surface of said housing means so as to contact with saidmovable contact blade member in a break circuit position thereof.
 10. Anelectric contact switching device according to claim 7, which furtherincludes a conductive plate member, and in which said housing meansincludes a recessed portion for housing said first conductor means, saidconductive plate member being mounted on said recessed portion andconnected to said second conductor means.
 11. An electric contactswitching device according to claim 7, wherein said second externalconnecting means is a metal cylindrical member fixed to said housingmeans and connected with said second conductor means.
 12. An electriccontact switching device according to claim 7, further comprisingelectromagnet means housed within said housing means so as to actuatesaid first conductor means.
 13. An electric contact switch in accordancewith claim 7, wherein said conductive material is applied by plating.14. An electric contact switch in accordance with claim 13, wherein saidconductive material is applied by coating.
 15. An electric contactswitching device comprising in combination a first external connectingmeans dielectric means for supporting said first connecting means;firstconductor mean having a switching contact member connected to said firstexternal connecting means for switching a first conductor with saidswitching contact member; housing means for supporting and housing saidfirst conductor means, and said dielectric means wherein said housing isconstructed from a resin and wherein said housing is covered by ametallic layer which reinforces said housing; second external connectingmeans; said conductor means connected to said exterior connector means;and said second conductor means being in electric contact with saidmetallic layer which reinforces said housing.
 16. An electric contactswitching device in accordance with claim 15, wherein said metalliclayer is plated onto said housing.
 17. An electric contact switchingdevice in accordance with claim 15, wherein said metallic layer iscoated on to said housing.
 18. An electric contact switching device inaccordance with claim 15, further including a shield member mounted overa compartment which contains said switching contact member of saidhousing means.
 19. An electric contact switching device in accordancewith claim 18, further including a cover placed over said compartmentand said shield for enclosing said compartment.
 20. An electric contactswitching device in accordance with claim 19, wherein said cover ismetal plated and is used as a shielding member. .Iadd.
 21. An electriccontact switching device which confines R-F within said device,comprising in combination:first external connecting means supported at abottom portion of said device; first conductor means having a switchcontact member connected to said first external connecting means forswitching a first connection with said switch contact member; housingmeans for housing said first conductor means wherein said housing meansis constructed from a material which is electrically conductive; secondexternal connecting means; and second conductor means connected to saidsecond external connecting means, wherein said second conductor means isin electrical contact with said housing and is contiguous with saidhousing means for shielding said R-F. .Iaddend. .Iadd.22. An electriccontact switching device which confines R-F within said device,comprising in combination: first external connecting means supported ata bottom portion of said device; first conductor means having aswitching contact member connected to said first external connectingmeans for switching a first connection with said switching contactmember; housing means for housing said first conductor means, whereinsaid housing means is constructed from an insulating material having anelectrically conductive material provided thereon; second externalconnecting means; and second conductor means connected to said secondexternal connecting means, wherein said second conductor means is inelectrical contact with said conductive material of said housing meansand is contiguous with said electrically conducting material on saidhousing means for shielding said R-F. .Iaddend. .Iadd.23. An electriccontact switching device which has a first external connecting meanssupported at a bottom portion of said device, comprising incombination:first conductor means having a switching contact memberconnected to said first external connecting means for switching a firstconductor with said switching contact member; housing means for housingsaid first conductor means, wherein said housing means further comprisesa metallic material which reinforces said housing means; second externalconnecting means; and second conductor means connected to said secondexternal connecting means, wherein said second conductor means is inelectrical contact with said metallic material which reinforces saidhousing means and is contiguous with said housing means for shieldingsaid R-F. .Iaddend. .Iadd.24. The electric contact switching deviceaccording to claim 21, further comprising means for electricallyisolating said first and second conductor means from one another..Iaddend. .Iadd.25. The electric contact switching device according toclaim 22, further comprising means for electrically isolating said firstand second conductor means from one another. .Iaddend. .Iadd.26. Theelectric contact switching device according to claim 23, furthercomprising means for electrically isolating said first and secondconductor means from one another. .Iaddend.